March 2, 1876] 



NA TURE 



347 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications.^ 



Prof. Tyndall on Germs 



I AM very glad I wrote to you putting my questions to 

 Prof. Tyndall, It has drawn from him a letter, full of all 

 sorts of hints and prophecies and information and pleasant 

 observations on details with which I had not thought of 

 troubling him ; and there is even a delicate bit of flattery 

 for poor me, of whom the Professor knows nothing. It is 

 really quite a gem of a letter, a beautiful example of that 

 "tour piquant" referred to by M. Pasteur, which the 

 Professor gives to everything he touches, and which we 

 at home know how to value as well as any Frenchman, 

 There is only one fault in it, and that is that the Pro- 

 fessor, in the exuberance of his kindness, has unfortunately 

 forgotten to answer my modest questions. But why does he 

 liken himself to Horatius, and talk of enemies yet to be dealt 

 with ? Horatius did not sing his paean before going into battle. 

 And how can Prof. Tyndall have any enemies ? I thought that 

 scientific investigators were all brothers. I regarded Prof. 

 Tyndall as a brother keeping a bright look out due north, and 

 Dr. Bastian as a brother with his eye firmly set towards the 

 south, while Dr. Sanderson seemed to me to be a remarkably 

 silent brother gazing somewhere about sou'-sou'-west-and-by- 

 south- a-quarter-south. 



But to be serious. Briefly put, the situation seems to be this. 



Prof. Tyndall has propounded a theory — no mere speculation 

 raising a trifling controversy to be setded privately with Dr. 

 Sanderson or Dr. anybody else, but a momentous theory on 

 which, as he says, " the lives of men depend," and the truth of 

 which it concerns all men to sift It is not addressed to any 

 scientific coterie, but widely published for the benefit of the 

 outside world, the like of me among the rest. 



The theoiy as propounded stands or falls with the assertion 

 that when, with due precautions, an organic fluid is boiled for a 

 few minutes in a flask, which is then hermetically sealed, it is 

 impossible to obtain bacterial putrefaction. 



What Prof Tyndall declares to be Impossible, that Dr, San- 

 derson declares Uiat he has done. 



If Dr. Sanderson is right there is an end of the theory, and 

 the lives of men must rest on some other basis. 



If Prof. Tyndall is r ght. Dr. Sanderson (not to put too fine a 

 point upon it) has blundered in his very careful experiments. 



Anxious to know where I should look for the truth, I ven- 

 tured to ask Prof, Tyndall which alternative he adopted. Instead 

 of helping me out of my difficulty he has responded with a 

 flourish of rhetoric about not crossing swords with Dr, Sander- 

 son. It is plainly from no want of courtesy that Prof. Tyndall 

 has declined to satisfy my curiosity. He can't help being 

 courteous ; and to the class to which I belong — simple students 

 who hang upon the lips of Professors for their scientific sus- 

 tenance — he invariably overflows with courtesy. 



I am sure he would have answered me if he could. 



Even now I should be grateful (and so I believe would many 

 more of us outsiders) if on second thoughts he should resolve to 

 put his rhetorical sword into the unadorned scabbard of common 

 sense, and kindly try to answer three plain questions : — 



1, Does he accept Dr. Sanderson's experiments, and give up 

 his theory ? 



2, Does he reject Dr. Sanderson's "experiments as untrust- 

 worthy, and why ? 



3, Can he suggest any third view which will reconcile his 

 theory with established facts ? 



Unless Prof. Tyndall feels constrained by his regard for human 

 life to give me a reply, I will not press him to do so, if it would 

 be in the least embarrassing. Only, if there is to be an answer, 

 I hope this time it will be direct to the point. Perhaps, after 

 all, it is not absolutely necessary. Silence is sometimes more 

 eloquent than speech, 

 Feb, 19 Inquirer 



[This letter was unavoidably delayed last week. — Ed.] 



The Mechanical Action of Light 

 In his recent lecture at the Royal Institution upon the Me- 

 chanical Action, of Light, Mr. Crookes stated that his investi- 



gations into this subject had enabled him to measure the repulsive 

 force of light, and he calculated that the sun's light exercised a 

 repulsive force upon the surface of the earth of 3,000 millions of 

 tons, a force sufficient, he said, to drive the earth into space, 

 were it not for the attraction of gravitation. 



Let us look for a moment at this conclusion of Mr. Crookes, 

 Granting that gravitation and a (hypothetical) tangential force 

 cause the planets to revolve round the sun, the continuous action 

 of a repulsive force emanating from the sun and impinging upon 

 the surfaces of the planets, would cause them to spin round upon 

 their axes just as a ball spins round when it is propelled along a 

 resisting surface. This rotation would be in the same direction 

 — right to left — as the revolution of the planetary bodies in 

 their orbits. 



But such an explanation of the rota':ion of the planets upon 

 their axes will not, unfortunately, hold good, as upon this hypo- 

 thesis their axes ought to be perpendicular to their orbits, whereas, 

 with the exception of Jupiter, the equators of the planets are 

 largely inclined to their orbits. If, then, the rotatory movement 

 of the earth is not caused by the friction of a repulsive force eman- 

 ating from the sun, it is clear that the effect of the 3,000 millions of 

 tons which Mr. Crookes says continuously press against that half of 

 the earth's surface which is exposed to the sun's rays, would be 

 to retard not only the earth's diurnal rotation, but also its annual 

 movement round the sun. Now there is no evidence whatever 

 of retardation from any such cause, either as regards the earth 

 or the planets with whose movements we are most familiar. 



I do not in the least question that under certain circumstances 

 light may repel solid, liquid, or gaseous bodies, and, indeeJ, if 

 Mr. Crookes' general conclusions be confirmed, it may be found 

 that the rapid extension of the tails of comets as they approach 

 the sun may be due to the repulsive action of the sun's rays. As 

 this force would be inversely as the square of the distance, the 

 effect of the sun's light, acting in a straight line upon the highly 

 attenuated matter of which a comet's tail is composed, would 

 repel it with enormous velocity in a direction opposite to the 

 sun as the comet approached its perihelion. 



Manchester, February George Hicks 



Metachromism and Allied Changes 



The laws of metachromism, enunciated by Mr. W, Ackroyd 

 (in his recent paper read before the Chemical Society, N.^ture, 

 vol. xiii. p. 298), have an apparent parallel in the order of 

 colours shown by various series of combinations ; there being but 

 few exceptions to the following rale, in its application to binary 

 compounds. Increase of the electto-ttegative elemetit produces a 

 colour change towards the red end of the spectrum, and vice versa. 

 Thus the sub-oxides are generally blue, and the per-oxides yellow ; 

 the sub-sulphides white or yellow ; and the per-sulphides red. 



The examples which lead to this generalization are as 

 follows : — 



K4O blue grey, K,© white, T^O^ chrome yellow. 



KjS reddish yellow, K2S2 orange, KjSj liver brown, 



KgCl blue, KCl white, Na and Rb chlorides the same. 



Na40 blue, NajO yellowish white, Na-^Og orange. 



CS4O blue, CsjO white. 



(H4N)2S2 yellow, (H^NjgSs orange yellow. 



CeO white, Cefi^ fawn red. 



U3O4 green, U2O3 brick red. 



FeCl2 white, FeClg brown, 



CrjOj green, CrOj yellow green, CrOs red. 



MnO olive, Mn304 red brown, Mn^Os brown black. 



MnS dark green, MnSo brown red, 



SnO olive brown, SnO^ yellow. 



SnS blue grey, SnSj yellow. 



MoO purple brown, MoC^ dark brown, 



M0S2 lead grey, M0S3 dark brown, 



M0CI2 deep blue, MoC]4 dark red. 



WjOs blue, WO3 yeUow. 



SbjOj grey white, SbjOj pale yellow. 



SbjSa blue black, SbgSg orange yellow. 



BLjOs yellow, Bi^Oj brown. 



CUjjCljj white, CuClj liver colour, 



PbO yellow, Pb304 red, PbOg brown. 



PbS lead grey, PbSj red. 



TI2O yellow, TI.P3 brown, 



Hgl green, Hg 1 2 yellow or red. 



AujO dark green, AU2O3 brown. 



PtClj olive, PtCU orange. 



OsClj green, OSCI4 red. 



